Delay when using texture paint
UV Image Editor will always be faster with paint because it isn't held back by projection effects like culling, cavity mask, etc. Painting in the 3d view needs to be done with small brushes for faster paint daubs, as large brush radius can cause a memory choke while waiting to project and calculate all the pixels to be affected by the paint stroke. 

Also, a key factor here is how large your texture is and how many undo steps exist in your preferences. Decrease the undo steps or eliminate them altogether for the session and see if the memory spikes stop. The size of the texture and the bit depth can cause some issues with painting using projection in the 3d view, but you will see that the UV Image Editor handles them much easier. 

The key difference in these two options for paint is that the UV Image Editor is one texture at a time (display) but the 3d view can display all or one (GLSL/Material Draw mode vs. Multitexture) and you can use both to their advantage to get the best effects.